Wings on the wind

How do migrating birds know exactly when, and where, to go?

Imagine if, when you were very young and were utterly dependent on your parents
for protection and food, they had abandoned you suddenly to go overseas? Without
any written instructions as to where they’d gone, would you have been able
to follow their path once you’d grown strong enough to try?

Sound impossible? Not for the Bristle-thighed Curlew! When the chicks are just five
weeks old, the parents depart, heading for the tropics.1 Left behind in the marshes of the Alaska Peninsula,
the chicks gorge themselves on berries and insects. As their little bodies become
stronger, accumulating the all-important reserves of fat—fuel for the long
journey ahead—they frequently take to the air for short flights, as if in
premigratory practice.

The parents suddenly desert the chicks at the end of summer.

Then one day, the birds launch themselves into the sky, and, finding the right winds,
head off on the long nonstop flight south to their ancestral wintering grounds.
As with most migratory bird species, the curlew novices are on their own, without
a guide. Their parents and experienced elders have departed weeks earlier. Yet most2 of these first-year curlew pilots
will unerringly navigate the vast Pacific Ocean, descending with pinpoint accuracy
onto the mudflats and sandy beaches of islands in Fiji, Tonga and French Polynesia—their
new home.3

The chicks of another famous migratory species, the Short-tailed Shearwater (‘muttonbird’),4,5
must also navigate on their first flight without the assistance of experienced guides.6 Breeding in burrows on islands off southeastern
Australia, the parents suddenly desert the chicks at the end of summer. The parents
head north, riding the prevailing winds that will take them around the western Pacific
Ocean past Japan and Siberia, east around Alaska, and south down the western United
States, before they return across the Pacific for the next start of the Australian
summer breeding season.

Birdwatchers along the eastern Australian coast have observed as many as 60,000
shearwaters per hour flying past.

Without parents to bring them food, the abandoned shearwater chicks live on accumulated
fat for about two weeks. Becoming restless, they leave their burrows to test their
wings in the night breeze. Soon they find a suitable takeoff point on a cliff or
overhang, and plunge into their new element, somehow charting their way over vast
unfamiliar oceans to the other side of the world, months later finding their way
back to the very same island to breed. Birdwatchers along the eastern Australian
coast have observed as many as 60,000 shearwaters per hour flying past, arriving
back at their burrows within the same eleven-day period each year.

The ability of both juvenile curlews and shearwaters to navigate, untaught, to the
opposite hemisphere is astounding, but of the two, the curlew’s is probably
the more remarkable. While the Short-tailed Shearwater is renowned for the length
of its great journey (over 13,000 km (8,000 miles) from Australia to Alaska), the
Bristle-thighed Curlew’s flight of more than 8,000 km (5,000 miles) across
the Pacific is nonstop. Unlike seabirds like terns or shearwaters, which
can rest and feed along the way, the curlews will drown if they land on the ocean.

The Bristle-thighed Curlew’s flight of more than 8,000 km (5,000 miles) across
the Pacific is non-stop.

But the curlew’s incredible migration is exceeded by the Bar-tailed Godwit.
In midsummer, godwits nesting in western Alaska leave their breeding grounds and
congregate by the tens of thousands along the Alaska Peninsula, where they feed
on clams and other goodies from the intertidal mudflats. They gorge themselves until
the fat builds up into thick rolls under their skin—up to 55% of their total
weight.

Then they stop eating, and undergo an incredible internal change. Their intestines,
kidneys and liver shrivel up, shrinking to a fraction of their usual size (scientists
suspect this happens to many long-distance migrants). Laden with fuel, and with
lightened innards, the godwits take off by the thousands, flying south at around
72 km per hour (45 mph). Many will not stop again until they reach New Zealand,
a journey of 11,000 km (6,800 miles), lasting four or five days—believed to
be the longest nonstop bird migration in the world.

‘South for the winter’?

The popular Northern hemisphere notion that ‘birds fly south for the winter’
is somewhat misleading.

Just why do birds embark on these incredible journeys? The popular Northern hemisphere
notion that ‘birds fly south for the winter’ is somewhat misleading.

Birds do not leave an area merely because the weather is due to turn cold. Studies
show that migration is fundamentally about food supply, not temperature, as birds
that can continue to find enough to eat during the winter rarely migrate—e.g.
many ravens, which eat almost anything, have been known to survive in areas where
the temperature drops to –57°C (–70°F).

Birds that eat seeds are less likely to migrate than insectivorous birds.

In contrast, almost all the bird species that do migrate depend upon weather-sensitive
food supplies. Insect-eating songbirds would have a hard time trying to find bugs
once the winter snows arrived; similarly, wading birds, once their marshes became
sealed by ice. Birds that eat seeds are less likely to migrate than insectivorous
birds, and tend not to travel as far. Among the insect-eaters, too, there are differences—birds
that eat flying insects must migrate to significantly warmer or even tropical areas,
in contrast to birds that eat terrestrial insects.

So a determining factor in migration is the deliberate moving towards something
beneficial rather than a moving away from something unpleasant. It’s
not just a simple, north-to-south-and-back-again affair either. As the Short-tailed
Shearwaters show, the oceans of the world are criss-crossed by masses of migrating
birds, few of which are traveling to avoid bad weather. Often they are traveling
from isolated breeding islands to rich feeding grounds close to the opposite pole.7 The Arctic Tern’s quest for food
takes it over 35,000 km (22,000 miles) in a single year—the world’s
longest migration route. Nesting at high northern latitudes, it annually travels
south to fish through the Antarctic summer, enjoying a greater percentage of daylight
in its life (thus more hours in which to hunt) than any other creature on Earth.

The Arctic Tern’s quest for food takes it over 35,000 km (22,000 miles) in
a single year—the world’s longest migration route.

Over land, migration can have a strong east-to-west component, e.g. in the USA,
Red-head Ducks may migrate from Utah to the Atlantic for the winter, while Harlequin
Ducks that nest in the Rocky Mountains migrate west to the Pacific. Within the tropics,
hummingbirds, parrots and toucans [pictured, left] undertake great migrations which
often coincide with the mass blossoming of nectar-laden flowers or the ripening
of fruit or grass seeds. In the mountains of Central and South America, it is estimated
that a fifth of the tropical bird species seasonally migrate between highlands (where
nectar and fruit are abundant only part of the year) and warmer, wetter lowlands.

Of course, the fluctuations in food supply (seeds, nectar, insects), which apparently
spur bird migration, are themselves tied to the seasonal variation in the Earth’s
climate. This seasonal variation occurs because our planet’s axis is tilted
off the vertical by an average of 23.5°, so as the Earth orbits the sun, first
the Northern hemisphere then the Southern hemisphere are inclined toward the sun,
producing the seasons.8

Despite being closely linked to food supply, not temperature, it appears that regular
bird migration journeys are not usually driven by hunger. In fact, for most migrating
species, a bird is at its fattest just before beginning its migration—notably
the Bar-tailed Godwit.

Flaptastic fat

Traveling by their own power over several thousand kilometres nonstop, the godwits
and other long-distance migrants demonstrate a feat of strength and endurance that
far outranks other animals or man. The key to this is the reservoirs of energy-providing
fat built up during the premigratory feeding frenzy. The fat is secreted into special
cavities between tissues and organs. It therefore does not affect the weight
or bulk of muscles that must remain in top-class condition for flying.

The fat is secreted into special cavities between tissues and organs. It therefore
does not affect the weight or bulk of muscles that must remain in top-class condition
for flying.

And this is no ordinary fat. Ordinary fat contains much water, but fat stored by
migratory birds is much more highly concentrated, containing little water and thus
is much lighter. But isn’t less water a problem for a long-distance flyer,
unable to stop for a drink? No—because as the fat ‘burns’, combining
with oxygen, enough water is produced to enable the birds to fly for long periods
without drinking.

Incredibly, it appears that these long-distance migrants store exactly
the right amount of fat required for the journey. The Golden Plover, for example,
puts on an extra 70 g (2.4 oz) of fat, 50% of its normal bodyweight, which is precisely
the right amount it needs to travel from Alaska to Hawaii, a journey of 4,500 km
(2,800 miles), taking around 88 hours at about 51 km per hour (32 mph).9 Also, it’s as if the amount of fat stored has somehow
been ‘calculated’ to allow for the energy-saving boost in efficiency
on these long-distance flights, compared to normal flight—an efficiency arising
from ‘flying in formation’.

Birds of a feather

When the Golden Plover flies over ocean, it flies in flocks in the classical ‘V-formation’,
in which, on average, each bird saves 23% of the energy that would be used when
flying alone.

A Golden Plover converts 0.6% of its bodyweight into motion and heat per flight
hour. (By comparison, a helicopter and a jet plane need, in relation to their weight,
seven times and 20 times more fuel respectively, than a Golden Plover.)9,10 This means that with 70 g (2.4 oz)
of accumulated fat at the start of its flight, a single Golden Plover would crash
into the sea 800 km short of its destination, Hawaii. But, in reality, the tropical
haven is attained safely because when the Golden Plover flies over ocean, it flies
in flocks in the classical ‘V-formation’, in which, on average, each
bird saves 23% of the energy that would be used when flying alone. (This is not
the case for the bird at the apex,11
but birds take turns at that position, and thus ‘share the load’—something
Christians are also exhorted to do (Galatians
6:2).)

Not all migrating birds fly in the energy-saving ‘V-formation’, but
many birds do migrate in (often huge) flocks. In one night, radar showed an estimated
12 million songbirds passing Cape Cod, USA, on their way south. In November 1995,
an estimated 50 to 80 million ducks and geese pushing south overwhelmed the air
traffic control radar at the Kansas City and Omaha airports.

Time to fly

Perhaps by sensing changes in atmospheric pressure, birds can perceive the approach
of major weather systems.

Somehow birds know when to migrate, as well as where.12 Scientific knowledge about bird migration, particularly
the ocean-goers, is still scanty, but a picture of the factors that might trigger
migration is emerging. It is now believed that before a bird migrates, there must
be at least two elements present: a genetic predisposition13 and one or more environmental triggers.

Researchers have identified in songbirds that changing day length is a major environmental
factor, but it is now being realized that there is a whole suite of interacting
factors, such as barometric pressure, temperature, windspeed and direction. The
heaviest hawk flights, for example, occur after the passage of a cold front, with
lowering temperatures, rising barometric pressure, and associated brisk updrafts.
In the case of the aforementioned ducks and geese which closed the Midwestern US
airports, they were observed the previous day to be pouring south under sunny skies,
i.e. the day before an especially strong blizzard blasted out of the Canadian
prairies, pushing the birds along like a giant wave. It has been suggested that,
perhaps by sensing changes in atmospheric pressure, birds can perceive the approach
of major weather systems.

A built-in compass

The ability of migratory birds to fly to their destination with such precision requires
two abilities: orientation (knowing direction) and navigation (knowing when to change
direction). The first requires some kind of compass; the second needs a map. One
without the other is useless—it seems migratory birds have both. The mechanism
of birds’ innate direction-finding capacity has puzzled scientists for years.
At various times it has been mooted that birds navigate by the sun, the stars, and
geographical landmarks. All of these have been shown to be true but these
abilities all appear to be learned by experience—e.g. pigeons raised out of
sight of the sun and exercised only on overcast days cannot navigate by the sun,
but can still easily find their way. Conversely, pigeons that had learned to navigate
by ‘solar compass’ have a harder time navigating on cloudy days.

There is considerable evidence that birds primarily use some kind of built-in ‘magnetic
compass’.

So while birds apparently can learn to use a whole range of environmental cues for
navigation, there is considerable evidence that birds primarily use some kind of
built-in ‘magnetic compass’. It has even been suggested they carry some
kind of built-in ‘magnetic map’ of the Earth. Certainly, they are sensitive
to the slightest differences in intensity of the Earth’s magnetic field. How
can this be? Following the discovery of magnetite crystals in magnetically sensitive
bacteria in the 1970s, magnetite has also been found in the nasal cavities of several
species of migratory birds (as well as honeybees and other organisms with a ‘geomagnetic’
sense). But new evidence shows that birds do not simply fly on a constant magnetic
compass course but continually change their heading so as to fly the most efficient
route. (See Tripping the flight fantastic.)

Birds appear to be using a whole suite of magnetic, solar, stellar, atmospheric
and geographical cues.

Researchers now acknowledge that there is no one simple unified theory of how birds
can navigate so precisely. They appear to be using a whole suite of magnetic, solar,
stellar, atmospheric and geographical cues.

In the beginning … ?

How did this fantastic capacity to navigate across the globe come into being? According
to the theory of evolution, birds are the result of millions of years of chance processes,
mutations and natural selection. Evolutionist ornithologists suggest that migratory
paths began to ‘evolve’ as birds pushed ‘farther and farther north
each year as ice-age glaciers retreat[ed], returning in winter to a traditional
non-breeding ground that lies further away with each generation.'14 Though that might sound plausible enough, it does not
account for how a godwit first encountered far-flung islands such as New Zealand.
And how did a Bristle-thighed Curlew first find tiny Rangiroa Atoll in the vastness
of the Pacific? Nor does it explain how such migratory paths become ‘imprinted’
in the genes so that chicks can follow the ancestral migratory routes without guidance
from experienced birds. The smallest migratory hummingbird, with a brain scarcely
larger than a seed of corn, can navigate a flawless course over immense distances.
Yet this marvel of migration is supposed to have come about by an undesigned process!15

The creationist must also think carefully about exactly how such fantastic migratory
pathways originated. Caged nightingales have been observed fluttering on the north
wall of their cages in spring, and south in autumn. This urge to fly
in a particular direction seems to be inherited.13
This is why migratory chicks are able to follow ancestral routes. It is easy to
postulate that migratory instincts and capacities were all preprogrammed into the
original created kinds. But the Earth’s geography has been massively changed
by the global Flood. How could directional information useful in the pre-Flood world
still be relevant afterwards?

It is possible that God programmed the original kinds with the instinct to migrate,
but without a rigidly fixed ‘mental map’. In some amazing way, the programming
involved the capacity to adapt to changes in topography (and presumably food supplies)
in an inheritable fashion.

English birds oriented on a compass heading of 273° (i.e. towards London) while
the chicks of German-caught blackcaps tried to fly on a traditional heading of 227°,
i.e. towards Spain.

A possible clue to a mechanism for such adaptation is provided by blackcaps, which
normally migrate from Norway and western Europe to the Mediterranean and Africa.
However, since the 1950s, British birdwatchers have noticed more and more blackcaps
coming to England during the winter rather than to Spain. Researchers took 40 of
these birds to breed them in captivity in Germany, along with a separate group from
the normal blackcap migratory population. When the offspring were monitored in special
laboratory facilities, those of English birds oriented on a compass heading of 273°
(i.e. towards London) while the chicks of German-caught blackcaps tried to fly on
a traditional heading of 227°, i.e. towards Spain.

It is thus likely that in centuries past, a few migrant blackcaps always strayed
to Britain, the victims of a mutation in their genetic code controlling orientation.
Natural selection had formerly weeded these out, but in recent decades, winters
in Britain have been warmer, and there has been a huge increase in winter food,
e.g. backyard bird feeders.

Perhaps many of today’s migratory routes came about in such a way, as the
‘correct’ routes were selected for from among the variation built-in
at Creation for this purpose. Bird migration is such a bewilderingly complex phenomenon,
however, that at present, we can do little more than speculate about the details
of how these incredible post-Flood migratory routes arose. Meanwhile, we would be
wise to acknowledge what God’s Word tells us in relation to migration and
feeding of birds.

Even the stork in the sky knows her appointed seasons, and the dove, the swift and
the thrush observe the time of their migration—Jeremiah 8:7.

Ultimately, we read that it is the Lord who provides food for the raven when its
young cry out for lack of food (Job
38:41). Indeed, all the animals and birds look to God to give them their
food at the proper time (Psalm
104:21, 24, 27–28;
136:25;
145:15–16;
147:9). In light of these verses, it is interesting to note the surprise
of ornithologists who observed (across a range of species) that young migrant birds,
encountering the tropics for the first time, ‘showed an almost uncanny ability
to find their species-specific habitat with no discernible fumbling around.’16 Evolutionary ornithologists might
also do well to ponder the words of rebuke that the Lord spoke to Job: ‘Does the hawk take flight by your wisdom and spread his wings
towards the south?’ (Job
39:26).

But perhaps the most telling verse comes from Jeremiah 8:7,
which says, ‘Even the stork in the sky knows her appointed
seasons, and the dove, the swift and the thrush observe the time of their migration’,
and concludes: ‘But my people do not know the requirements
of the Lord.’

See you next year?

The practice of ‘banding’ birds’ ankles1 may have started almost accidentally, when Henry IV
of France lost one of his trained Peregrine Falcons around 1595, and the marked
bird showed up the following day on the Mediterranean island of Malta. In 1710 a
grey heron carrying a leg ring from Turkey was caught in Germany by a falconer’s
bird. And in the early 1800s, a Pennsylvanian resident tied a light silver thread
to the leg of nesting phoebes, subsequently confirming his theory that the same
individuals returned year after year.

Banding has now grown to the point where, in North America alone, more than 56 million
birds have been banded in the last 100 years—three million of which were recovered.

Banding has shown not only that migratory birds often return to precisely the same
tree to nest each year, but also that they show similar loyalty to their wintering
site on the other side of the globe.2

Weidensaul, S., Living on the wind: Across the hemisphere
with migratory birds, North Point Press, New York, pp. 38–43, 1999. Return to text.

The homing instinct of pigeons fascinated Charles Darwin, who
wondered if pigeons hauled in crates far from home somehow memorized the twists
and turns in the road as they felt them. (It wasn’t until many years later
that ‘retracement navigation theory’, as it was known, was finally disproved.)
Return to text.

Tripping the flight fantastic

Radar-tracking satellite-based telemetry allows the flight paths of individual birds
tagged with tiny transmitters to be recorded continuously. Using such technology
to study various migrating Arctic shorebirds has revealed an incredible fact. When
migrating, these birds fly along the Earth’s great circle routes (orthodromes)
rather than on a constant magnetic compass course (loxodrome), which is easier to
navigate but results in longer flight distances.1,2

The great circle route conserves energy because it is the shortest distance to the
final destination. But it is navigationally demanding because birds migrating along
these orthodromes must continuously change their compass course because their route
intersects successive longitudes.

How do they do it? Mathematicians have calculated that if one uses a time-compensated
sun compass without resetting one’s internal clock while traveling across
successive longitudes (i.e. moving into different time zones), the resulting route
would be an orthodrome, i.e. the shortest flying distance. This navigational trick
is especially beneficial to the Arctic shorebirds, because, the closer one is to
the polar regions, the better this short-cut strategy works. The birds also know
how to compensate for crosswinds, automatically changing their directional heading
to account for any sideways deviation. There are still many more mysteries to explore,
as the Arctic shorebirds do not return in spring along the same routes used in autumn—an
observation the evolutionary researchers say ‘testifies to the complexity
of the global orientation performance of migrating birds.’

Day or night?

Not all birds fly to their destination non-stop.1
Hawks migrate only during the daytime, gliding vast distances from one thermal to the
next.

But much bird migration happens at night. And not just nocturnal species like owls,
but hundreds of otherwise day-active species—sandpipers, swans, songbirds
and wading birds.

For many years, man’s only clue to the extent of nighttime migration was by
‘moon-watching’—i.e. counting the silhouettes of birds passing
in front of the moon over a given period.2

It was not until the 1950s that it was realized that radar could detect flocks of
migrant birds. They showed up as diffuse green blobs (‘ghosts’) crossing
the monitor—the same ‘radar angels’ that had puzzled, worried
and even awed the military during World War II.

Weidensaul, S., Living on the wind: Across the hemisphere
with migratory birds, North Point Press, New York, pp. 16,30,35,36, 1999. Return to text.

A full moon covers about 1/347.45 of the visible sky.
Therefore, five moon-silhouetted birds in 10 minutes equates to 30 per hour; multiplied
by 347.45 equals about 10,420 birds per hour passing overhead in a band about 2.4
km (1½ miles) wide. Return to text.

Further Reading

References and notes

Weidensaul, S., Living on the wind: Across the hemisphere
with migratory birds, North Point Press, New York, p. 13, 1999. Unless otherwise
indicated, information presented here is sourced from this reference.
Return to text.

Hazards abound on the long journey, including storms, predators
and exhaustion. Nowadays the list includes radio towers and cross-country powerlines—thousands
of dead birds can be found littering the ground near these in the morning—as
well as lighthouses and brightly illuminated buildings. Return to text.

Captain Cook encountered the Bristle-thighed Curlew on Tahiti in
1769. For a hundred years afterwards, scientists assumed it was a permanent resident
there, unaware of its annual sojourn in Alaska. Return to text.

So named because they were an important source of meat (‘mutton’)
for the early British settlers in Australia. Return to text.

Shearwaters are members of a ‘family’ of great ocean-traveling
birds popularly known as ‘petrels’, which also includes the many species
of albatross. (The term ‘petrel’ is a diminutive meaning ‘Little
Peter’—so named because the pattering of their legs and webbed feet
across the surface of the water (during take-off, presumably) seemed to be an echo
of the Apostle Peter’s experience of walking on water, recorded in
Matthew 14:28–30.) Return to text.

Warm equatorial waters tend to have less food than the cooler oxygen-rich
waters at high latitudes. Return to text.

Pronounced seasonal variation has been in place at least since
the time of the Flood of Noah’s day (Genesis
8:22). Seasons have existed since the Creation Week (Day 4—see
Genesis 1:14), though seasonal extremes were possibly milder pre-Flood.
Return to text.

The Blackpoll Warbler, on its 5,600 km (3,500 miles) migration,
will have flapped its wings about three million times. If burning standard motorcar
fuel, its fuel economy would be 0.33 ml per 100 km (720,000 miles per US gal.).
Return to text.

Flying becomes progressively easier the further back a bird flies
in the ‘V-formation’. Return to text.

Not all bird migrations are annual. The Snowy Owl normally lives
near the Arctic Ocean, but every decade or so it makes winter incursions as far
south as Texas. This was once thought to coincide with population crashes of its
favoured prey, the lemming, but recent research has cast doubt on this linkage as
too simplistic. Return to text.

Evidence for this has come from studies of various species (e.g.
juncos, blackcaps) where migratory and non-migratory ‘races’ of the
same subspecies occur. In blackcaps, researchers were able to selectively breed
out the migratory urge within just three generations. Return to text.

The supposed evolutionary ancestry of birds is still hotly debated
by evolutionary scientists. Evolutionist bird expert Alan Feduccia summed up their
confusion: ‘The true origin of birds is still up in the air.’ (Cited
in Creation23(2):5, 2001.) Return to text.

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Readers’ comments

Cameron M.,Australia, 17 October 2012

Reading through this and pondering other articles about the major crust upheavals from The Flood. Could the larger migration paths be due to the major continental shifts (moving land masses that were near to each other further away)? God would have programmed the initial kind to follow a set compass course (more or less)...even after 6500 years they still do. Just maybe Post Flood the paths are now longer; but call upon created (and 2000 old year dormant) DNA coding to awaken and allow for the processes of fat build up etc.

Or just maybe they have had long paths the whole time.

Just a thought.

Melki H.,Indonesia, 17 October 2012

Thank you for this knowledge CMI, Dr. David, God Bless you.

Ian T.,Canada, 17 October 2012

Good interesting article. I don't need these things to prove to me there is a God, but they are nice to reconfirm what I already know. Our God is an awesome God!

Gary J.,United States, 17 October 2012

Thank you for this wonderful compendium! The wisdom of our creator is so far beyond our wisdom even when considering this one small aspect of the creation.

I thought of a different explanation for the Great Flood's effects on migration. Prior to the Flood, birds may or may not have had to migrate. But because God knew from the beginning that the geography of the earth as well as its climate would be vastly different after the Flood, he may have created birds with all their migration abilities whether or not they needed them at first. It would not be beyond God's abilities to update (even to this day) birds' "mental maps" of the earth or "mental paths" to follow. After all, he continues to sustain his creation until Judgment Day, so I don't think this violates God's rest from creating which began on Day 7.

Mark E.,Australia, 18 October 2012

This also leads me to wonder about the speed of the spread of plant life due to the droppings of migrating birds. Do they eat the same foods at both destinations? What role did they have in spreading or maintaining the food sources at either destination? What beneficial impact does the influx of bird life have on the local predators at each location?